TEAC CD-C68E six-disc CD-ROM changer

Review date: 2 February 1999.
Last modified
03-Dec-2011.

(Note: As you can see
above, this is an old review; IDE CD
changers like this one only work
right if you're using Windows 98 or
earlier. Maybe ME, definitely not
2000 or anything later. They work as
a single drive, and you can manually
mount and unmount discs in different
slots, but there's no way to make
them work properly.)

The TEAC CD-C68E is a six disc 8X CD changer - it holds
six discs, but can only read one at a time. It fits in a standard 5.25 inch
drive bay, just like any other CD-ROM drive, and it runs from the same IDE
interface as every other cheap CD-ROM drive. It has an average
seek speed of 190mS, not counting disc-changing
time.

On the front are six buttons, one for each CD slot, each with a status
light, and a volume control and headphone socket. It costs less than $350
(Australian dollars) for the bare drive.

I've been living with a C68E for some months now, and I love it.

Setting up

Installing the C68E is no harder than installing a standard IDE CD-ROM
drive. It's slightly longer than a standard CD-ROM drive, as this
comparison shows, but your case would have to be pretty darn cramped for it
not to fit.

When people first see it they tend to marvel at the fact that six
discs and a changer mechanism fit into a regular 5.25 inch drive bay, but
fit it does, with no problems. The C68E is a little longer than a standard
CD-ROM drive, but there was still plenty of room behind it in my modest
midi-tower case. Like any other IDE device, it can be set to "master" or
"slave"; if two IDE devices are plugged into one IDE channel (all current
PC motherboards have dual IDE channels) one must be the master and the other
the slave. Screw in the drive, plug in the IDE and power cables, and the
audio cable to the sound card if you like, and you're done.

Windows 98 recognises the C68E automatically. This was the first time
I'd installed something in Windows, seen six identical devices show up in
the Device List, and actually been pleased. As far as Windows
is concerned, one C68E is six drives, all the same. No driver installation,
no messing around; it just works.

Using it

You feed the C68E its discs through a slot reminiscent of a car CD player
- press the button for the slot you want to put the disc in, and the little
dust cover flips up and the appropriate light flashes orange and green,
alternately. Push the disc in half-way and the C68E pulls it the rest of
the way, closes its dust cover and checks the disc out. When it's successfully
read the disc, the light turns solid green; if the disc is illegible, the
C68E spits it out again. To eject a disc, just push its button. Out it comes,
and the C68E leaves the door open for a replacement disc for the slot. If
you don't want to insert one, just press the button again to close the door.

Loading all of the slots this way is done in seconds. The slot-load system
could, conceivably, result in disc damage if used often enough, but the
whole idea of a changer is that you don't have to swap
discs all the time. Put the discs you need all the time into the C68E and
forget them. They'll be there when you need them. You won't even be able
to leave them behind if you take the computer somewhere else.

The C68E is largely idiot-proof; it automatically rejects discs inserted
upside-down, and it won't try to eject a disc if there's already an ejected
disc sitting in the slot.

Accessing a disc that happens to be the one currently loaded is exactly
like accessing the disc in a regular 8X CD-ROM drive. If you want to access
a disc that isn't already loaded, you have to wait for
a few seconds while the changer chunka-chunks the old disc out and the new
disc in. The changing and spin-up process only takes from four and a half
to five seconds, depending on how many slots the changer has to traverse.
Just looking at the root directories of the discs can be done instantly,
provided the discs have already been accessed once in that session; the
C68E caches the root directory contents.

Problems

There are some caveats. The C68E takes about 30 seconds to chunka-chunk
its way through all six discs. It will do this at least twice in every computing
session; once when you power up or reset the computer (the boot process
continues while this happens - everything doesn't pause while the changer
shuffles discs), and once the first time your operating system decides to
take stock of all of its drives (which, in Windows, pretty much DOES cause
everything else to pause). Windows 95/98 does not do this by default when
it starts up; it generally does it the first time something opens a file
requestor or otherwise demands a drive list. To avoid a 30 second chunka-chunka
session the first time I try to open a file, I've stuck a shortcut to My
Computer in the Windows\Start menu\Programs\Startup directory. This doesn't
make the problem go away, but it gets it over with when I boot the computer.
I think an extra six CD-ROM drives is well worth a 30 second slower system
startup time.

If you're running two or more applications which simultaneously want
to access different discs in the changer, it would flog hopelessly. Realistically,
though, I don't know how this could happen, except in a network server with
many people accessing its resources. With a five second swap time, occasional
swaps don't hurt overall performance much.

The C68E's rather languid 190mS 1/3rd stroke seek
speed is another problem, though not in my opinion a major one. Using
a slowish device like this as your primary CD-ROM drive could prove slightly
annoying, but I don't think that's the C68E's niche; it works better as
an adjunct to an existing, faster CD-ROM drive. Slow seek speeds aren't
that bad, anyway; do your really care if a CD-flogging
operation that's done in 20 seconds on a faster drive takes 35 on the changer?

The C68E also can't handle CD-single sized discs - and comes with a warning
sticker on the front which says as much. Since practically nobody uses these
little discs, who cares? Again, if you keep your regular single disc drive,
there's no problem; pretty much all single disc drives work fine with singles.

The only way I can see a C68E causing real difficulties is if it stops
working, because I have no idea how much fiddling would be required to get
the discs out of it if the eject mechanism failed.

Overall

Anybody who's annoyed about swapping game CDs and reference CDs and application
CDs who knows what other kinds of CD in and out of their single CD-ROM drive
will love a CD-C68E. Don't throw away your current CD-ROM; with the dual
IDE channels of current PCs, anyone with three or fewer currently installed
IDE devices will be able to install a C68E as well. Keep whatever disc you're
using intensively in your single disc, higher speed CD-ROM drive, and keep
all the ones that get accessed regularly but not too heavily in the changer.
For under $350 (Australian dollars), this is a marvellous product.

Pros:

Cons:

Six CD-ROM drives for under $350!

Dead simple installation and operation.

30 second startup delay

Not terribly fast

Glossary

8X: NEC invented the "X" terminology
for describing CD-ROM drive speeds, and it's now spilled over into DVD-ROM
drive descriptions as well. The number before the X tells you the drive's
speed as a multiple of the speed of a first generation CD-ROM drive, which
could transfer 150 kilobytes of data a second. So an 8X drive can pump 1200
kilobytes per second. This suggests that current "40X" speedsters are good
for 6000 kilobytes per second. Well, yes and no. Mainly no.

There are two basic ways for a CD-ROM drive
to work; Constant Linear Velocity (CLV) and Constant Angular Velocity (CAV).

A CLV drive changes its speed of rotation according to the head
location - it spins the disc faster when the head's reading from the middle
of the disc. It does this in order to maintain a steady data transfer rate.

Audio CD players have to be CLV, because audio demands a constant
data rate, but CDs store data at a constant density per unit length all
over the disc. Since there's thus more data per revolution on the outside
of the disc than the inside, you have to change the rotation speed to keep
the transfer rate constant.

An audio CD player's rotational speed varies from about 210 to
539 revolutions per minute from the outside to the inside; first-generation
"1X" CD-ROM drives are exactly the same.

But for CD-ROM data transfer, you don't need to maintain a steady
data rate - the faster the better. As long as the drive is always at least
as fast as it has to be for a given application, everything's fine. This
is the philosophy behind CAV.

A CAV drive maintains the same revolutions per minute wherever
the head is. Since data on the CD is laid down at the same density per inch
all over the disc, this means that the drive delivers data faster when the
head is at the edge of the disc than when it's closer to the centre.

LP records (remember those?) are CAV - they're 33 and a third
RPM all the way, and get away with it because the inner tracks are more
densely recorded than the outer ones.

In order to make them sound more impressive, the speed of a CAV
drive is invariably quoted as the speed it can manage when reading the outer
edge of a CD.

The outermost edge of the data storage area on a CD has a circumference
of about 366mm. The innermost circumference, however, is only 135mm.
So a CAV drive with a given rating for the outermost edge will have a speed
for the innermost edge only about 37% of that rating; a "36X" CAV drive
has a minimum speed of only about "13X". The halfway point, where half of
a full disc's data lies inwards of the head and half of the data lies outwards,
is about 60% of the way out; here, the 36X drive will have roughly "22X"
performance.

This will not be its average speed over all discs, though. CD
data is recorded starting in the middle of the disc and moving to the outside.
This means CAV drives are incapable of achieving their maximum performance
on any disc which is not completely full - about 650Mb of data. For the
same reason, they won't perform at full speed on "CD-single" sized discs.
Since many discs aren't completely full, the actual average performance
of a CAV drive, taken over all CD-ROMs, is about half of its rated speed.

Some mid-speed drives use a mixture of CAV and CLV; CAV for the
outside of the disc, and CLV to spin the disc faster for the inner tracks.
This is not possible with current superfast CAV drives; a 40X drive screams
along at more than 8000RPM. If it tried to maintain the same linear velocity
for the inner tracks, it'd be doing more than 21,000 RPM. The fastest current
hard drives have a rotational speed of 10,000RPM (all hard drives are CAV),
and that's with finely machined, 80mm aluminium platters on a very straight
spindle, not 120mm stamped plastic discs held in a clamp.

There is practically no consumer storage hardware that can handle
the full data transfer rate of a modern CD-ROM drive, but the ludicrous
maximum speed means that more of the disc will be accessible as fast as
the computer can handle it - a 40X drive delivers about 2200 kilobytes per
second, even on the centre tracks. Just don't believe the hype.

Seek speed: Seek speed
is the length of time it takes a disk storage device to move its read head
to the location of a given piece of information. Hard disk seek speeds are
now commonly lower than 10mS (milliseconds; 1000 milliseconds to the second),
but CD-ROM full-stroke seek speeds (the time it takes to get the head from
the middle to the outside) are seldom much better than 200mS. The seek speed
of CLV drives is made even worse by the fact that
they have to change the disc speed when accessing different areas, and this
takes a significant fraction of a second, too.

CD-ROM specifications which quote a "1/3rd stroke" seek speed
are telling you the time it takes for the head to be moved across a third
of the disc. This is a fair measure, because disc seeks in most cases do
average out well to a third of the disc, but it's important not to think
that a drive with an 85mS 1/3rd stroke speed is faster than one with a 250mS
full stroke speed.

Seek speed is the real issue in CD-ROM performance. Any current
drive can deliver data plenty fast enough - once it's got to it. With a
190mS 1/3rd stroke speed, the TEAC CD-C68E is not a very fast drive in this
regard.